A broadly applicable cure for HIV-1 infection has remained elusive, in part, because the virus is able to circumvent host adaptive and innate immune responses. HIV-1 commandeers cellular pathways for its replication and antagonizes host proteins that inhibit viral replication. The HIV-1 accessory proteins, Vif, Vpr, Vpu and Nef, direct the degradation or mislocalization of cellular proteins that interfere with viral replicatio and persistence. Vif, Vpr and Vpu all usurp cellular ubiquitin ligases to degrade specific cellular proteins and facilitate replication. Some targets of these accessory proteins are known, but others are as yet undefined. Elucidating these viral-host cell interactions may reveal new viral dependencies on cellular proteins as well as new host antiviral proteins and viral countermeasures, revealing potential targets for antiretroviral therapy. The proposed project specifically examines the interaction between Vpu and the cellular ubiquitin pathway, determining the extent to which Vpu acts as a suicide inhibitor when targeting cellular proteins such as CD4 for degradation, the consequences these effects have for HIV-1 replication including viral cell-to-cell transmission. In addition, this study develops a novel experimental system to investigate the effects of HIV-1 gene expression and Vpu specifically on the modulation of cellular membrane proteins and global ubiquitination and degradation of cellular proteins, with the goal of attributing particular effects to the accessory gene vpu in the context f the complete repertoire of viral gene expression. In determining the host cell proteins modulated by HIV-1, this study will provide a better understanding of how HIV-1 manipulates the cellular environment to facilitate its replication and evade the immune response, which in turn will inform the development of new antiretroviral therapies. This proposal is intended to support the career development and further training of the candidate, who aims to extend her expertise in the molecular biology of HIV infection to include proficiency in the acquisition and analysis of proteomics and ubiquitinomics data sets. This project is expected to identify new cellular targets of HIV that will facilitate the development of independent lines of research, providing the foundation for the candidate to pursue additional sources of funding and foster a career as an independent physician- scientist.